XRRA1 Targets ATM/CHK1/2-Mediated DNA Repair in Colorectal Cancer.

X-ray radiation resistance associated 1 (XRRA1) has been found to regulate the response of human tumor and normal cells to X-radiation (XR). Although XRRA1 overexpression is known to be involved in cancer cell response to XR, there are no reports about whether the expression of XRRA1 in tumors can adjust radioresistance. It is widely known that cell cycle arrest could cause radioresistance. We found that blocked XRRA1 expression could lead to cell cycle G2/M arrest by the regulation of cyclin A, cyclin E, and p21 proteins in colorectal cancer (CRC) and expression of XRRA1 reduced cell cycle arrest and increased cell proliferation in CRC. However, whether regulation of the cell cycle by XRRA1 can influence radioresistance is poorly characterized. Correspondingly, DNA repair can effectively lead to radioresistance. In our study, when cancer cells were exposed to drugs and ionizing radiation, low expression of XRRA1 could increase the phosphorylation of DNA repair pathway factors CHK1, CHK2, and ATM and reduce the expression of -H2AX, which is believed to participate in DNA repair in the nucleus. Crucially, our results identify a novel link between XRRA1 and the ATM/CHK1/2 pathway and suggest that XRRA1 is involved in a DNA damage response that drives radio- and chemoresistance by regulating the ATM/CHK1/2 pathway.